Process for the production of nodular cast iron



Nov. 26, 1957 J. A. CLARK 2,814,559

PROCESS FOR THE PRODUCTION OF NODULAR CAST IRON Filed April 23, 1953 Mag: IOOX Etch: None Hag: 500! Etch: Id Nita].

COMMENTS:

The upper photanicrograph shows the graphite which is in the nodular form. h

The lower photomicrograph shows the etched structure. The matrix consists of ferrite with a. few areas containing some spheroidal carbides.

JAMEfi A. CLARK mmvm.

'vaporization, or'of removing the slag.

United States Patent 1 2,814,559 PROCESS FOR THE PRODUCTION OF NODULAR CAST IRON James A. Clark, Snyder, N. Y. Application April 23, 1953, Serial No. 350,562 3 Claims. (CI. 75-53) This invention relates to an improved method for producing nodular iron and to the improved alloys produced thereby.

In recent years there have been tremendous advances in the art of strengthening and improving the general properties of iron by the addition of nodulizing agents to molten iron. These agents have the efiect of produc ,ing graphite nodules distributed throughout the metal,

without the necessity for any annealing of the cast metal.

One of the most successful nodulizing agents thus far discovered is cerium. Small amounts of cerium, added to the molten iron as pure cerium or as a cerium-rare earth metal alloy, have been found to have an extreme effect in producing the nodular arrangement of graphite with the accompanying desirable physical characteristics. Another additive commonly used for the same purpose is calcium carbide. Both of these additives, and the other common nodulizing agents, have been found to have several disadvantages. In the case of cerium and cerium alloys such as Mischmetal, there is usually difliculty in obtaining a thorough and even mixture of the additive in the iron. There is also the common problem of oxidation and volatility-many of the additives oxidize or vaporize before they can be distributed. Some additives, such as calcium carbide, involve further peculiar problems. For instance, when calcium carbide is used, a dry white powder rises to the top of the molten metal. This powder is thought to be calcium oxide. It has proved very difiicult to skim off this powder as a slag, and it has also been found that the powdery impurity appears in the finished casting as inclusions in the iron. These inclusions are visible to the naked eye, in the finished piece of cast metal. This weakens the iron and does not produce any offsetting beneficial characteristic.

All of these difliculties have seemed to result in one common undesirable characteristic in the final castings. This undesirable characteristic is the marked tendency toward an uneven distribution of the nodules in the iron. This uneven distribution of the nodules means uneven strength characteristics in the iron, with the result that castings were not uniform in properties and their strength was not closely predictable. These uneven strength characteristics can readily be foreseen in photomicrographs, since patches of flake graphite are usually visible between concentrations of nodules.

; The object of this invention is to provide an improved nodulizing agent which will produce a nodular iron of uniform characteristics, with no attendant problems of obtaining good distribution, of avoiding oxidation or A further object of the invention is to provide an improved method for producing nodular iron whereby an even distribution of thenodulizing agent is easily obtained. Another object of the invention is to provide an im- "proved method for fluxing molten iron prior to casting,

while obtaining a nodulizing action at the same time. Still another object of the invention is to improve the properties of gray iron and to favorably influence the structure of white iron and the stability of white iron 'structure. These and other objects of the invention are achieved by the use of Rare Earth Fluoride as the agent for producing the desired characteristics in the final alloy. A

combination of Rare Earth Fluoride with calcium silicon "with improved're'sults.

I Patented Nov. 26, 1957 Rare Earth Fluoride is a recognized trade name used by the major suppliers of rare earth salts. The term, Rare Earth Fluoride, is used throughout the specification and claims to denote a specific commercial product now available on the market. This product is produced to a standard analysis and is actually a mixture of rare earth fluorides. Commercial Rare Earth Fluoride is standardized to contain 47% of cerium fluoride. The balance is composed of the fluorides of lanthanum, praseodymium, and neodymium, with very small amounts of the fluorides of other rare earths. The metallic cerium content of Rare Earth Fluoride is 31.8%. The commercial product is a very fine powder.

The critical component appears to be cerium fluoride,

although insuflicient data is available to state this with certainty. Cerium fluoride can be used interchangeably with Rare Earth Fluoride to produce very similar results. Commercial cerium fluoride is available in two grades. Cerium Fluoride, Tech., is about pure, and Purified Cerium Fluoride is about 98% pure. Either of these products may be substituted for Rare Earth Fluoride to produce similar good results. At present, however, Rare Earth Fluoride is about one-third as expensive as the more purified cerium salts. It is therefore more attractive to use Rare Earth Fluoride. Some of the other rare earth fluoride appear to be similar in action to cerium fluoride, and there is no evidence that their presence is undesirable.

When an equivalent amount of Rare Earth Fluoride or cerium fluoride is substituted for the cerium metal added to an iron batch as a nodulizing agent, there is a marked superiority in the castings containing the fluorides over those containing metallic cerium or Mischmetal. For instance, a casting to which Rare Earth Fluoride has been added shows a more even distribution of nodules and a complete lack of macroscopic inclusions. The iron may therefore be said to be cleaner, in the sense that there are substantially no macroscopic inclusions. A plausible theory in explanation of the clean appearance is that the fluoride salts have a fluxing action which separates impurities from the molten metal and renders removal of all of the impurities much more easy because they form a readily separable, coherent slag. The more even distribution of nodules is probably attributable to the even distribution of the nodulizing agent in the molten metal,

which is achieved easily when the powdered Rare Earth Fluoride is used rather than Mischmetal.

This more even distribution is attained by adding the powdered fluoride salt to the molten stream of metal as it enters the pouring ladle.- An alternative method which is just as satisfactory comprises placing the fluoride salts in the bottom of the ladle and pouring the molten metal into the ladle on top of the salt. Mischmetal is added in lump form, and usually much of the Mischmetal is oxidized before the lumps are melted. Also, it is obviously much more diflicult to obtain an even distribution of lumps than of a powder.

The. improved properties of alloys formed by using Rare Earth Fluoride may be readily seen from an inspection of the data from a few test heats. Three batches of nodulizing mixtures, for addition to molten iron, were made up as follows:

MIXTURE #1 Lbs. Magnesium ferrosilicon"; 5.3 Zirconium alloy (35%) .6

Rare Earth Fluoride 1. 5 Calcium silicon 3.2

MIXTURE #2 Lbs. Magnesium ferrosilicon 5.3 Zirconium alloy (35-%) Calcium silic 3.2

.3 MIXTURE #3 Lbs.

Magnesium ferrosilicon 5.3 Zirconium alloy (35%) .6 Mischmetal .75 Calcium silicon 3.2

It willbe seen that Mixture 1 contains magnesium ferrosilicon, which is a conventional inoculant, as the main ingredient, plus a zirconium alloy in a minor amount, plus calcium silicon. These three ingredients are present ineach test test mixture. They are conventional additives in wide use today. In addition to these components, Mixture #1 contains Rare Earth Fluoride. Mixture #2 is a control batch, having no special nodulizing agent. Mixture #1 contains Mischmetah The amount of Mischmetal in Mixture #3 is approximately the amount necessary to provide metallic cerium in an amount equal to that present as the fluoride in the Rare Earth Fluoride in Mixture #1.

These three mixtures were used to inoculate different portions of similar masses of molten iron. Tests on castings from the so-treated iron show that the nodular iron produced was most satisfactory from Mixture #1. The castings produced by using Mixture #3 were not up to the high standard obtained when Mixture #1 was used. As would be expected, when the control, Mixture #2 was used, much less satisfactory results were obtained. Details of these tests are summarized in Table I.

The drawing shows the fine nodules produced in the casting obtained from Heat 3049, to which 2% of Mixture No. 1 had been added. The upper photomicrograph shows a non-etched specimen at 100x. The nodular graphite is plainly visible. The etched lower photomicrograph, at 500x, shows the ferrite matrix and more details of the nodular graphite structure.

This unique process is not confined to any critical ratios of additive to the iron, other than those necessarily imposed by the final composition desired. When Mischmetal or metallic cerium are used, some of the metallic additive is oxidized before casting and freezing, but through experience, skilled artisans know how much additive to use to produce the desired final cerium content. The same situation obtains when the fluoride salts are used, but there is a much smaller loss due to oxidation, and hence a less close control need be maintained.

The combination of Rare Earth Fluoride with calcium silicon in the additive has some beneficial effect. Thus, an iron to which was added 2% calcium silicon and 1% Rare Earth Fluoride showed excellent modulation. The combined action of these two ingredients was superior to the action of either one without the other.

I claim:

1. A process for producing nodular iron having in its solid state nodules of graphite uniformly distributed therethrough which comprises adding to a molten iron containing about 0.06 percent sulfur by weight, based on the Table I Amount Base iron composition Deflection Mixture of mixand trans- Ctr, Heat No. No. ture verse break inches BHN used, TC Si Mn Load percent 1 1 3.36 2.39 0. 75 {g gg j 18 1 1% 3.34 2.37 0.77 18 286 18 293 3. 30 2.32 1 2 0.76

{W 12 3055 1 2 3.44 2.18 0. 74 d a In addition to the above properties, Heat No. 3049 was found to have the following outstanding characteristics:

It will thus be seen that this invention provides an improved process for incorporating nodulizing agents in iron. In addition to the metallurgical advantages of producing a cleaner casting with a uniform nodule distribution, the use of Rare Earth Fluoride is a much more economical way to incorporate cerium in iron than by the use of Mischmetal. However, it should not be assumed that this invention merely provides a new method for incorporating cerium in iron. This invention does much more than provide a new vehicle for cerium inoculation. This invention provides a flexing action, apparently caused by the fluoride salts, which makes it more easy to remove the scum from the molten metal. This fluxing action, in combination with the even distribution of the fluoride .powder, combine to produce superior castings.

weight of the iron, a powdered crude mixture of Rare Earth Fluorides containing about 47 percent cerium fluoride and the balance consisting essentially offluorides of lanthanum, praseodymium and neodymium, distributing said powdered Rare Earth Fluorides uniformly throughout said molten iron, allowing said Rare Earth Fluorides to form a slag on the surface of said molten iron with impurities present in the iron, removing said slag and solidifying said molten iron.

2. The process of claim 1 wherein about 2 percent of said mixture of Rare Earth Fluorides, based upon the weight of said molten iron, is added thereto.

3. The process of claim 2 wherein about 2 percent of calcium silicon and about 1 percent of said mixture of 5 Rare Earth Fluorides, each based upon the weight of said molten iron, is added thereto.

References Cited in the file of this patent UNITED STATES PATENTS 

1.A PROCESS FOR PRODUCING NODULAR IRON HAVING IN ITS SOLID STATE NODULES OF GRAPHITE UNIFORMLY DISTRIBUTED THERETHROUGH WHICH COMPRISIES ADDING TO A MOLTEN IRON CONTAINING ABOUT 0.06 PERCENT SULFUR BY WEIGHT, BASED ON THE WEIGHT OF THE IRON,A POWDERED CRUDE MIXTURE OF RARE EARTH FLUROIDES CONTAINING ABOUT 47 PERCENT CERIUM FLUORIDE AND THE BALANCE CONSISTING ESSENTIALLY OF FLUORIDES OF LANTHANUM, PRASEODYMIUM AND NEODYMIUM, DISTRIBUTING SAID POWDERED RARE EARTH FLUORIDES UNIFORMLY THROUGHOUT SAID MOLTEN IRON, ALLOWING SAID RARE EARTH FLUORIDES TO FORM A SLAG ON THE SURFACE OF SAID MOLTEN IRON WITH IMPURITIES PRESENT IN THE IRON, REMOVING SAID SLAG AND SOLIDIFYING SAID MOLTEN IRON. 